feat: implement ledger-based timestamp validation for deadlines

[greatest0fallt1me]

Description:

Use ledger close time (or equivalent) for event end, bet deadline, and dispute window so that timing is deterministic and consistent with the chain.

Requirements and Context:

• Must be secure, tested, and documented
• Should use env.ledger().timestamp() (or equivalent) for “current time” in deadline checks
• Should store and compare event end, bet deadline in same time domain
• Should document that clients must use ledger time for display/estimation
• Must not rely on off-chain timestamps for enforcement
• Should integrate with existing event and bet deadline logic

Suggested Execution:

1. Fork the repo and create a branch

   git checkout -b feature/ledger-timestamp-validation

2. Implement changes

   • Write contract: replace any non-ledger time with ledger timestamp
   • Update validation and storage; add documentation and NatSpec-style comments

3. Test and commit

   • Run tests; cover deadline at ledger boundary, testutils ledger advance
   • Include test output and security notes

Example Commit Message:

feat: implement ledger-based timestamp validation for deadlines

Guidelines:

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 48 hours